Process for the manufacture of palladium (ii) halides from metallic palladium



United States Patent F 48,639 US. Cl. 23-87 Int. Cl. C01g 55/00, 1/06 Claims 0 ABSTRACT OF THE DISCLOSURE Halides of the bivalent palladium produced by treating metallic palladium having a large surface area with oxygen in the presence of carboxylic acids and in the presence of metal halides or ammonium halide,

The present invention relates to a process for the manufacture of palladium (II) halides from metallic palladium.

It is known that palladium (II) compounds, especially palladium (II) chloride (PdCl and tetrachloropalladate (II) (with the anion [PdCl are used as catalysts in processes concerning the oxidative conversion of olefins, for example ethylene, into carbonyl compounds, for example acetaldehyde, or into unsaturated esters, for example vinyl acetate. However, to assure the economy of these processes, it is necessary to reconvert the metallic palladium formed in the oxidative conversion of the olefin in a simple manner into the compounds of the bivalent palladium.

The halides of the bivalent palladium, especially the chlorides, are generally prepared by the chlorination of metallic palladium at high temperatures, by dissolution in aqua regia and subsequent evaporation to dryness, by a treatment with oxidizing nitrogen-oxygen compounds, for example nitric acid or the oxides of nitrogen, or by contacting oxygen or chlorine with the palladium metal in the presence of hydrochloric acid or primary aliphatic alcohols.

However, a disadvantage of these processes is that they require the use of strong acids and/or oxidation agents whose corrosive properties require special apparatuses, and security measures. For this reason, these processes, especially in the case of reactions which occur with the oxidation of olefins, cannot be carried out or with difiiculty only.

For processes for the oxidative conversion of olefins into carbonyl compounds or carboxylic acid alkenyl esters it has, therefore, been attempted to reconvert the metallic palladium formed into compounds of the bivalent palladium in the reaction mixture itself by means of oxygen or oxygen-containing gases in the presence of suitable oxidation transfer agents. As oxidation transfer agents there are used salts, especially the chlorides of heavy metals which may occur in several oxidation stages, for example the chlorides of copper, iron, manganese, cobalt or lead. However, these processes require in most cases special reaction conditions, such as strongly acid pH values and elevated pressures. Moreover, in the presence of heavy metal halides there are frequently observed side reactions of the olefin, for example the formation of dimerization products and/ or halogen derivatives of the olefin.

Now we have found a process for the manufacture of halides of the bivalent palladium which consists essentially in treating the metallic palladium with oxygen of oxygen-containing gases in the presence of carboxylic acids containing 1 to 4 carbon atoms and in the presence of halides of metals of Group I, II or III of the Periodic Table, of ammonium and the mixtures thereof at a temperature within the range of from 10 to 150 C.

As palladium there are used advantageously types of palladium which have a large surface, for example palladium black or finely divided palladium on carriers, such as carbon, graphite, aluminum oxide or silicic acid.

Halides of metals which may be used for carrying out the process according to the present invention are, preferably, the chloride and bromides of metals of Groups I, II and III of the Periodic Table, for example, the chlorides and bromides of lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, barium, aluminum as Well as those of ammonium and mixtures thereof.

As carboxylic acids those containing 1 to 4 carbon atoms may advantageously be used, but above all formic acid, acetic acid and propionic acid or the mixtures thereof.

When carrying out the process according to the present invention, the metallic palladium having a large surface is heated with solutions of the chlorides or bromides of the said metals in dilute or concentrated carboxylic acid at a temperature within the range of from 10 to 150 (3., preferably from to 140 C. while simultaneously contacting oxygen or oxygen-containing gases with the solutions containing the palladium. Per gram atom of the palladium metal, there are used advantageously 1 to 150, preferably 20 to gram moles of the inorganic salt. The concentration of the carboxylic acid may be within the range of from 5 to 100 percent, depending on the solubility and the amount of the metal halides applied. Advantageously there are used pure carboxylic acids or carboxylic acids having as high a concentration as possible. However, especially in the case of a low solubility of the metal halides, the process can also be carried out in carboxylic acids which have been diluted with water.

The oxygen or oxygen-containing gases, such as air, may be contacted with the solutions containing the palladium by introducing the gas at normal pressure or at an elevated pressure. In many cases the palladium, especially when using palladium carrier contacts, contains such an amount of oxygen that it is suflicient simply to heat the palladium contact with the solutions of the metal halides in carboxylic acids and the introduction of oxygen or oxygen-containing gases may be dispensed with wholly or partially.

When working according to the process of the present invention, the palladium passes into solution as palladium (II) compound, and that-depending on the metal halide concentration applied-as palladium (II) halide, as tetrahalogenpalladatefll) or as mixture of these compounds. The palladium(II) compound can be isolated from the solutions in a suitable manner, for example by concentration or crystallization at a low temperature. However, the solutions which contain the palladium (II) compounds may also, if necessary or desired after the separation of undissolved palladium or palladium carrier substances, be reused as such as catalysts in processes for the oxidative conversion of olefins.

An advantage of the process of the present invention is that in the oxidation of the palladium, or in the preparation of palladium(II) halides and/or tetrahalogenpalladates(II), the operation may be carried out under mild conditions thus avoiding the use of strongly corrosive oxidation agents or solvents. When Working according to the processes hitherto known, corrosions could be avoided only with difiiculty.

In addition to the preparation of the palladiurnUI) halides the process may be used especially'for the preparation of catalytically active solutions for the oxidative conversion of olefins and for the regeneration of 1 Example 1 grams of oxygen-free palladium black were heated, under reflux, with 100 ml. of a 1 molar potassium chloride solution in acetic acid of 50% strength. 50 liters of air were passed through the boiling solution over a period of one hour. After cooling, the solution obtained was separated from the undissolved palladium. The solution contained 37% of the palladium applied in the form of a palladiumflncornpound.

Example 2 5 grams of a pulverulent, oxygen-free palladium-carboil-contact having a palladium content of 4.4% were heated, under reflux, with 100 ml. of a 1 molar potassium chloride solution in acetic acid of 50% strength. 50 liters of air were passed through the boiling solution over a period of one hour. After cooling, the carbon dust was filtered off with suction and washed with ml. of acetic acid of 50% strength. The palladium content of the solution amounted to 97 milligrams, which corresponded to 44% of the palladium applied.

When 5 grams of the aforementioned palladium-carbon-contact were treated by the same method with 100 ml. of acetic acid of 50% strength (without potassium chloride) or with 100 ml. of a 1 molar potassium chloride solution in water (without acetic acid), only 0.05% of the palladium used were dissolved with the use of the alone acetic acid of 50% strength, and with the aqueous potassium chloride solution only 0.7% of the palladium were dissolved in the form of palladium(II)chloride.

Example 3 5 grams of a pulverulent palladium-carbon-contact having a palladium content of 4.9% and an oxygen content of 0.21% were heated with 100 ml. of a 1 molar potassium chloride solution in acetic acid of 50% strength without further introduction of air until boiling commenced. After cooling, the carbon dust was filtered oif with suction and washed with 10 ml. of acetic acid of 50% strength. The palladium content of the solution corresponded to 93.3% of the palladium applied.

If there were used in this example, instead of the 1 molar potassium chloride solution, solutions of other salts in 100 ml., respectively, of acetic acid of 50% strength, the values were obtained as listed in the table following hereunder.

Percent Pd Salt concentration: dissolved 1 molar LiCl 82.0

1 molar LiBr 45.2

1 molar NaCl 81.4

1 molar NH Cl 91.5

0.5 molar MgCl 55.3 0.33 molar AlCl 94.0

0.5 m. KC1+0.5 m. NH Cl 96.5

4 Example 4 In the manner described in Example 3, 10 grams of a pulverulent palladium-carbon-contact having a palladium content of 4.9% by weight and an oxygen content of 0.21% by weight were heated with 100ml. of a 1 molar potassium chloride solution in acetic acid of 50% strength until boiling commenced and then filtered immediately. On cooling the filtrate, crystals of potassium tetrachloropalladate(II) precipitated which were filtered off and dried. The yield of crystalline potassium tetraohloropalladate(II) amounted to 68.2%, calculated on the palladium applied. The mother liquor could be reused to dissolve out more palladium from a fresh contact.

Example 5 5 grams of a pulverulent palladium-alumirru m-oxide contact having a palladium content of 2.2% were heated, under reflux, according to the method described in Example 2, over a period of 1 hour with 100 ml. of a 1 molar potassium chloride solution in acetic acid of 50% strength while passing in 50 liters of air during this period- After cooling, the solution was filtered from the remaining residue. The palladium content of the solution was 32.5%, calculated on the palladium applied.

We claim:

1. A process for the manufacture of a member of the group consisting of a chloride and bromide of bivalent palladium, which consists essentially in treating finely divided metallic palladium having a large surface area with a member of the group consisting of oxygen and an oxygen-containing gas in the presence of a carboxylic acid having from 1 to 4 carbon atoms and in the presence of a halide member of the group consisting of a chloride and bromide of a metal of a member of the group consisting of Groups I, II and III of the Periodic Table, of ammonium and the mixtures thereof at a temperature within the range of from 10 C. to 150 C., and wherein 1 to 150 gram moles of halide are used per each gram atom of metallic palladium.

2.. A process as claimed in claim 1, wherein the carboxylic acid used is formic acid, acetic acid or propionic acid or the mixtures thereof.

3. A process as claimed in claim 1, wherein finely divided palladium in the form of an oxygen-containing palladium-carrier-contact is used.

4. A process as claimed in claim 1, wherein the temperature is within the range of from to 140 C.

5. A process as claimed in claim 1, wherein 20 to gram moles of the metal halide are used per each gram atom of metallic palladium.

References Cited UNITED STATES PATENTS 3,210,152 10/ 1965 Van Helden et al 23-87 3,294,484 12/1966 Ellis 2387 EDWARD STERN, Primary Examiner.

US. Cl. X.R. 23-50 

